This invention relates to silicon carbide coatings on substrates and more particularly to a method for making such coatings by converting silicon carbide precursor polymers into silicon carbide while minimizing thermal stress on the substrate.
Various types of processes and equipment require materials which have hardened surfaces, resistance to corrosion and the capability to operate under high temperatures. Such material requirements can be fulfilled by refractory materials such as silicon carbide in applications such as claddings for high temperature service, hard facings, and bulk structural material. It is not, however, possible to place thin layers of silicon carbide on many kinds of substrates owing to the processing temperatures involved and the low melting degradation temperatures of the substrates to which one might wish to apply the silicon carbide coating. For example, U.S. Pat. No. 4,298,558, issued Nov. 3, 1981 to Baney et al. discloses a method of preparing an article coated with ceramic material in which a substrate is coated with a mixture of polysilane and fillers and the substrate is subsequently heated in an inert atmosphere or vacuum to a temperature in the range of 1200.degree. C. to 1600.degree. C. until the coating is converted to a silicon carbide ceramic. This process precludes the use of many substrates which would be adversely affected by the temperature involved.
Certain silicon carbide pre-ceramic polymers are known to decompose into silicon carbide when heated to a temperature in the range of 1200.degree. C. to 1600.degree. C. Various types of substrates can be coated with these polymers and subsequently heated to form silicon carbide-coated articles. A process which would provide for the necessary heating of the polymer coating without producing undue thermal stress on the substrate would greatly expand the number of suitable substrates. If the heating is sufficiently localized and controllable, a variety of sizes and shapes of substrates can be used and intricate patterns of silicon carbide can be created on the substrate.